Ediacaran Embryo Fossils Are Algae or Animal, Not Bacterial

FTIR microspectroscopy of Ediacaran phosphatized microfossils from the Doushantuo Formation, Weng’an, South China

Authors:

1. Motoko Igisu (a, b)
2. Tsuyoshi Komiya (a)
3. Mika Kawashima (c)
4. Satoru Nakashima (c)
5. Yuichiro Ueno (d, e)
6. Jian Han (f)
7. Degan Shu (f)
8. Yong Li (g)
9. Junfeng Guo (g)
10. Shigenori Maruyama (d, e)
11. Ken Takai (b, e, h)

Affiliations:

a. Department of Earth Science and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153–8902, Japan

b. Precambrian Ecosystem Laboratory, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2–15 Natsushima-cho, Yokosuka 237–0061, Japan

c. Department of Earth and Space Science, Osaka University, 1–1 Machikaneyama-cho, Toyonaka-shi, Osaka 560–0043, Japan

d. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152–8551, Japan

e. Earth-Life Science Institute, Tokyo Institute of Technology

f. Department of Geology and Key Laboratory for Continental Dynamics, Northwest University, Xi'an 710069, China

g. School of Earth Sciences and Resources Management, Chang'an University, Xi'an 710054, China

h. Subsurface Geobiology Advanced Research (SUGAR) project, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2–15 Natsushima-cho, Yokosuka 237–0061, Japan

Abstracts:

Phosphatized microfossils from ca. 580 Ma from the Doushantuo Formation in the Weng’an region of South China were analyzed by Fourier transform infrared (FTIR) microspectroscopy for their chemical characterization. Two morpho-types of phosphatized embryo-like fossils (Megasphaera and Megaclonophycus) were analyzed, together with algal fossils. Transmission IR spectra of the microfossils have absorption bands of around 2960 cm− 1 and 2925 cm− 1, indicating the presence of aliphatic hydrocarbon (anti-symmetric aliphatic CH3 and aliphatic CH2), and have an additional band of around 1595 cm− 1, probably derived from aromatic moieties (aromatic C = C). In addition, IR microscopic mapping shows that aliphatic hydrocarbon and aromatics are distributed inside the embryo-like fossils. The embryo-like fossils appear to show three types of CH3/CH2 peak height ratios (R3/2) and aromatic C = C/CH2 peak height ratios (RC=C/2 values): (1) high-R3/2/low-RC=C/2 type (R3/2 = ~ 0.2–1.0 and RC=C/2 ~ 0–2), (2) low-R3/2/medium-RC=C/2 type (R3/2 = ~ 0.2–0.6 and RC=C/2 = ~ 1–4); (3) low-R3/2/high-RC=C/2 type (R3/2 = ~ 0.2–0.6 and RC=C/2 ~ 1–8). All three types are contained in both Megasphaera and Megaclonophycus. Raman spectra for the carbonaceous matter within the rock sample show a similar degree of thermal alteration, indicating the organics were embedded in situ prior to thermal maturation. The IR spectroscopic differences might reflect differences in original organic compositions of microorganisms, and/or immediate post-mortem alteration. This suggests that the origins of phosphatized embryo-like fossils are more diverse than was previously recognized on the basis of their morphology. A comparison of R3/2 and RC=C/2 values in the embryo-like fossils with those of the algal fossils and the extant microorganisms indicates the possible interpretation that some of the embryo-like fossils belong to animal embryo, others are algae, but none of them originate from bacteria.